The present invention relates to a coupling for transmitting force between two relatively movable members. More particularly, the present invention relates to a frictional force transmitting means for use in combination with two relatively movable members.
Most friction energized devices used in the handling of pipes, bars, rods, etc., employ toothed penetrators as grip elements. The grip elements are laterally loaded by means of wedges, cams, linkages, or other such force systems to force the penetrators into gripping engagement with the pipe, rod, etc. While such devices are generally successful in terms of their ability to grip, they suffer from disadvantages which in certain cases can be quite serious. For example, the use of such gripping devices in oil field operations wherein the gripping devices are in the form of pipe tongs, pipe slips, etc., present a problem in that often the toothed gripping element will dig into the casing, drill pipe, tubing, etc., forming sharp edged notches. Particularly when handling drill pipe or tubing, the use of such devices may result in the drill pipe failing while under load due to the sharp edged stress raising cuts in the pipe wall caused by the toothed gripping devices. Moreover, most commonly used friction gripping devices or couplings are not readily adaptable to irregularly shaped surfaces due to the fact that the rigid tooth penetrators are not able to uniformly engage the undulating surface of the member sought to be gripped.